Electron beam tube



Oct. 17, 1939. H. E. HoLLMANN ELECTRON BEAM TUBE Filed Dec. 18, 1956Illlzlllltl /5' INVENTOR Patented Oct. 17, 1939 UNITEDV STATES l2,176,589 ELEoTRoN BEAM TUBE Hans Erich Hollmann, Berlin, Germany,assignor to Telefunken Gesellschaft fr Drahtlose Telegraphie m. b. H.,Berlin, Germany, a corpora.-

tion of Germany Application December 18, 1936, sentirne. 116,524

In Germany January 1.621.193.6-

The invention relates to a thermionic cathode tube having an electrondischarge controlled by an electron lens whereby saiddischarge has the4form of a flat, circular disc with the cathode in the center.

In the cross field tube described in my United States Patent 2,164,922issued July 4, 1939, there is disclosed a thrrnionicV discharge tubewith a lenticular electron beam substantially concentrated in a planeextending between two annular anodes and deflected at right angles toits median plane by a transversal cross eld. The tube operates inaccordance with the so-called cross control principle by which, asdistinct from the ordinary grid controlled space charge tubes in whichtheplate current variations are produced by longitudinal intensitycontrol of the discharge, the plate current variations are produced byspecial displacement of the Zone yof impingement of the beam on the twoanodes. The entire cross eld tube has rotational symmetry about thecathode as an axis, the axial thermionic cathode being surrounded inring fashion by the electrodes of the cylindrical electron lens serving-for the production of the lenticular electron beam, by the controlelectrodes for producing the cross field controlling the beam, andby thetwo annular anodes. In they center plane of these ring electrodes theelectrons ilow almost in the form of a flat lenticular disc reduced insizeV towards the periphery.

For controlling the brilliancy in cathode ray tubes, for instance Vfortelevision purposes, the principle has been utilized that an electronbeam produced by an electron lens may be controlled in intensity by anelectron lens without undergoing appreciable Vderornriation of itsgeometrical form. By this principle the intensity of the cathode raybeam is modulated in accordance with the image currents by means ofastriction or Wehneltv cylinder without thereby causing avariation inthe velocity or configuration of the beam. Since the striction cylinderdocs not absorb current and acts solely because of the potential fieldpassed by the electrons. the modulation takes place without requiringenergy. If in such. .a cathode ray tube the cathode ray beam instead ofirnpineing on a uorescent screen is thrown against a suitable absorptionelectrode or upon an anode, there ,is obtained an electron tube in whichthe current can be controlled in the same manner as by means 4of a gridwithout control energy being required. A practical advantage of thistype of control as compared with the space .charge control hitherto in.use is that in this type of control space .charge disturbances areentirely absentgand the characteristic oi .the tube is almostcornoletelylinear 'ir-ern .zero to the InaXiinurn current.

In ordery that in the' electron' bearn as high amperage as possible maybe utilized and to. ob-

tain the greatest feasiblersteepness of the characteristic withoutincreasing the specific current density beyond an ,allowable degree, theuse cfa flat bearn in place of a fine bearn as usedin oscillograph .andtelevision tubes for the production of a sharp uorescent spot ispreferred and obviously a sharp focusing inthe forrn of a line is notrequired.- Hoyt/raler2 the irregular field distribution in .such a -hatbeam andin the correspending electron lens system, especially at theedges. entails border ldis..trirloanoes in the beam and irregularitiesthe-characteristic of the tube,' ,especially in the pronounced` regionsof curvature. thereby limiting the practically allowthe forni oi a Yflatdisc .extending uniformly in all radialA directions from a cathodesituated in the center olf. the disc and riscontrolled in intensity byelectron optical means, Aside from the complete avoidance of borderdisturbancesi a beam dischargeuof, this v Shape has the great advantage'that the entire emission of the axial 'cathode can be fully utilized,-and that the electrons emitted from the v.cathode in` al1 directions areuniformly accelerated and controlled, and all obey the same 4.

electron-optical laws of resolution. l

The invention will better be understood by reference to the accompanying.drawing in which the gures are vertical sections of forms of disc beamtubes,` and in which FigureV l shows a tube with electron lens controlsystem; Figure 2 a modification utilizing a second electron lens systemat fixed potential as a screen; Figure 3 a modification utilizing twoelectron lens controls separated by an electron lens screen; and Figure4 a multiple tube in which three electrodevsystems as shown in Figure 1are positionedalong a common cathode and connected in cascade.

i The tube shape obtained. from employing the electron-optical currentand intensity control in rotational, symmetrical disc beam arrangementsis in general shown in cross section in Figure 1. The tube comprises theusual highly evacuated bulb Il] enclosing the electrodes, vone of whichis the axial cathode, which may be a lament, a

helix, or a metal tube coated with electron emitting oxides andindirectly heated by a heater insideit. 'I'he electron-optical controland concentration system or electron lens is arranged ringlike aboutthis axis, and in the example shown is in the form of an annularcondenser field produced by an annular control Aelectrode combinationconsisting of two rings I2 concentric with the cathode and constitutingelectrically a, single equipotential control electrode, as the ringsVare connected so that both are at the same potential, for instance anegative potential. The rings I2 are spaced to leave between them anannular slot in registry with an annular anode I3, which is a sheetmetal ring surrounding and concentric with the other electrodes and inposition to intercept the electron discharge passing through the'annular slot. The electrical field which is produced in the slot or gapbetween the control rings I2,v

which form a kind of cylindrical electron lens, effects a concentrationof the electron discharge which is emitted from the axial cathode in allradial directions and flows to the annular anode. The anode is connectedthrough a load circuit I4 to a battery I5,.,which also supplies' aninput circuit I6 connected to the control electrodes I2.

If a positive potentialis applied to the anode I3, and a negativepotential to the two control rings or plates I2, asharply limiteddisc-shaped or lenticular electron beam, indicated in crosssection bydotted lines, passes to and is focused on the anode. If the annularanode ls made ucrescent, for instance by a coating of a fiuorescentmaterial on its inner surface, the electron optical concentration andfocusing can be clearly seen, as a narrow stripe glows on the entirecircumference of the annular anode. If the negative potential oftheannular cross eld between the control rings I2 is varied with referenceto the cathode, the brightness offthe fiuorescent stripe also varies,showing that the electron density and hence also the plate'currentcorrespondingly'varies. An optical analogy would be the projection upona cylindrical surface of a line source of light through an annularcylindrical lens of which the curvature maybe varied at will. l

If an alternating control potential is applied to the ring controlplates I2 and in phase, as distinguished from the cross eldaccording tomy said copending application, in which alternating potential ofopposite phase-on the ring electrodes deflects the beam, the anodecurrent follows changes in the control potential with true amplitude andwithout` distortion. The transgrid action, or extent'to which the anodeeld acts upon the space between the cathode and the electron lenscontrol electrodes` I2 canin .practice be easily reduced to anunappreciable degree with sufficient spacing of the anodel from thecathode, as by placing the anode at the focal distance of thecylindrical electron lens, so that the quality of the tube is greatlysuperior to the grid tubes withspace charge control.

As shown in Figure 2, the transgrid action may also be substantiallyreduced in case of small tubes if a second shielding electrodecombination or electron lens which is maintained at a fixed potential isinserted between the control .field and the anode. The shieldingcylindrical lens may be two other ring electrodes similar to the controlelectrodes I2, or a sheet metal plate positioned transversely to thebeam and having a slot in the path of the beam; or preferably two pairsof sheet metal rings I'I and I8, the rings in each pair being of thesame diameter and concentric with the cathode, with their edges spacedto leave an annular slot, and the pairs of rings having differentpotentials, as shown, for instance, in Figure 2. The action of theselens systems can be considered as similarto that of a shield or screengrid in a multi-electrode tube with space charge, and as there, thequality of the tube is improved to a remarkable extent by these screenelectrodes.

As shown in Figure 3 there may be inserted between the cathode and theoriginal control field another control field by which the averageintensity of the electron beam can be aifected independently of thecontrol field. This other control field is, as shown in Figure 3,preferably produced by an electrode combination comprising two rings orplate electrodes I9 maintained at the same potential, and it may beshielded against the original control field between the rings I2 `by afurtherV screen electrode 20, preferably a tubular sheet metal electrodewith an annular slit or aperture. For such a control of the beamamperage and hence also of the steepness Yof the characteristicpractical possibilities of application are seen when the tube operatesby means of the plates I2 as a transmitter which can be modulated bymeans of the second control iield electrode I9, or Ywhen the degreeofamplification of the tube is to be controlled for'instance for thepurpose of automatic volume control or the like. In this connectionthere may also be considered the simultaneous amplification of twodiiferent frequencies by means of the two electrode combinations orsystems I2 and I9.

Finally the principle of the invention may also be readily applied tomultiple tubes so made that a long axial cathode common to severalelectrode systems emits several disc beams in planes parallel to eachother. One practical example of constructionV for multiple tubes isshown in Figure 4. The individual tube stages are for the sake ofsimplicity shown as made in accordance with the Figure `1, and in theexample represented they are connected in series in the manner of aresistance capacity amplifier in cascade. The interspace left betweenthe individual stages to avoid capacitive disturbancecoupling may toadvantage be protected against the entrance of electrons, preferably byshielding sleeves- 2i disposed along the cathode between stages, and thecoupling which may be present in spite of these sleeves can be reducedto a minimum by radial metal shields 22 constituting radial discextensions of the sleeves and extending between stages. The seriesconnection of the tube stages is conventional, including the loadresistors 23 and biasing resistors 24. Obviously the individual tubes orstages of this multiple arrangement may also be connected in many otherWays and combinations.

I claim:

1. An electron discharge device comprising a rectilinear cathode, asinge annular imperforate anode surrounding said cathode, an annularequipotential control electrode combination interposed between andconcentric with said cathode and anode and comprising a pair of parallel.fiat ringsI spaced to provide an annular slot extending transversely ofsaid cathode and bisected by the median plane of said anode, said ringsbeing positioned to form the discharge from said .cathode to said anodeinto a lenticular beam, and

an electron lens electrode combination interposed between said controlelectrode combination and said anode for focusing said lenticular beamon said anode in said median plane, said electron lens electrodecombination comprising two annular equipotential lens electrodecombinations of different diameters mounted concentric with said cathodeand between said control electrode combination and said anode, each ofsaid lens electrode combination having an annular slot aligned with theannular slot in said control electrode combination, the lens electrodenearest the control electrode combination being a tubular sheet metalelectrode with walls perpendicular to said median plane of said anode.

2. An electron discharge device comprising a cathode, a single annularimperforate anode surrounding said cathode, an annular equipotentialcontro-l electrode combination interposed between and concentric withsaid cathode and anode, said control electrode combination comprising apair of parallel flat rings extending transversely of said cathode andspaced to provide an annular slot bisected by the median plane of saidanode, a tubular sheet metal electrode surrounding said controlelectrode combination with its wall perpendicular to the median plane ofsaid anode and having an annular slot aligned with said annular slot insaid control electrode combination, and an annular equipotentialelectrode combination surrounding said tubular electrode and having anannular slot aligned with the annular slot in said tubular electrode,said electrode structure being adapted to form the discharge from saidcathode to said anode into a lenticular beam focused on said anode.

3. An electron discharge device comprising a rectilinear cathode, asingle annular imperforate anode surrounding said cathode, an annularequipotential control electrode combination interposed between andconcentric with said cathode and anode and comprising a pair of parallelflat rings spaced to provide an annular slot extending transversely ofsaid cathode and bisected by the median plane of said anode, said ringsbeing positioned to form the discharge from said cathode to said anodeintov a lenticular beam,

and an electron lens electrode combinations interposed between saidcontrol electrode combination and said anode for focusing saidlenticular beam on said anode in said median plane, said electron lenselectrode combinations comprising two sheet metal tubular electrodecombinations of dilerent diameters mounted concentric with said cathodeand between said control grid and said anode with their wallsperpendicular to said median plane of said anode, each of said tubularelectrode combinations having at the middle an annular slot aligned withthe annular slot of said control electrode and with imperforate portionson each side of said slot extending beyond the planes of said ilatrings.

4. An electron discharge device comprising a cathode, a single annularimperforate anode surrounding and coaxial with said cathode, and twoannular equipotential electrode combinations of different diameters,each comprising two flat rings of equal diameter spaced to provide anannular slot, said electrode combinations being mounted coaxially withand transversely of said cathode with said annular slots aligned andbisected by the median plane of said anode, and an equipotential tubularsheet metal electrode combination interposed between said annularelectrode .combinations with its wall perpendicular to said flat ringsand having an annular slot in registry with the annular slots in saidannular electrode combinations.

5. An electron discharge device comprising an elongated cathode, aplurality of cold electrode assemblies spaced along said cathode tocooperate with separate and distinct portions of said cathode, each ofsaid assemblies comprising an annular anode and an annular equipotentialcontrol electrode combination surrounding and coaxial with said cathodeand having an annular slot in registry with said annular anode, andmetal discs extending radially from said common cathode between saidcold electrode assemblies to electrostatically shield each of saidassemblies from the others.

HANS ERICH HOLLMANN.

